The resistivity of photoresistive or photosensitive materials varies according to the quantity of incident light. In other words, the resistance decreases as the incident light increases.
Prior art photoresistive materials generally comprise elements from groups II to VI of the periodic table of elements. For example, cadmium sulfide (CdS) or cadmium selenide (CdSe) are currently used in applications in the visible range, particularly due to their low cost. However, such materials are generally unfit for infrared applications. In this case, lead sulfide (PbS) may then be used.
Further, prior art materials have many disadvantages, among which their lack of stability in time, or their relatively long response time when the luminosity varies.
As for heat-resistant materials, their resistance or resistivity varies according to temperature. These materials may be based on metals or metal oxides. Unlike photoresistors, thermistors are generally stable along time.
The material developed by the Applicant is capable of sensing in the visible range as well as in near infrared. Further it has an electric resistance which decreases according to quantity of captured radiation. This material also enables to detect heat variations capable of reflecting as variations of the near infrared radiation emitted by a finger in the context of a tactile application.